A bond portfolio should be the backbone of every retirement savings plan. Governments and corporations sometimes issue debt-related securities into the financial markets to fund their operations. You can think of them as the lender if the "issuer" were the borrower and the investors the lender.

Bonds, like any other type of loan, come with interest payments in addition to the repayment of the principal amount, so they can provide a regular flow of income to those who invest in them. Because of this, they are beautiful to retirees looking to supplement their income after leaving the workforce. Bonds are outstanding for retirement since their value is less likely to fluctuate than an investment in the stock market.

Here is a quick summary of the best bond funds for retirement.

1. Vanguard Intermediate-Term Bond ETF

Businesses with tax-deferred retirement plans, such as individual retirement accounts, invest in Vanguard Intermediate-Term Bond ETF (BIV). This exchange-traded fund follows an index that includes U.S. government and corporate bonds and foreign bonds denominated in dollars. The terms are between five and ten years in length.

The total assets under management for the fund are $35 billion, spread across 2,040 different securities. Full returns for the year are 8% thus far. Due to its market-value weighting methodology and exclusion of agency mortgage-backed securities, BIV has a more significant allocation to U.S. Treasury notes than comparable bond ETFs. The cost to the customer is 0.05% as well.

2. iShares iBoxx $ High Yield Corporate Bond ETF

Investing in "junk" bonds could be a good idea if you do not mind taking some financial risks. Due to the high probability of default from the borrower, credit rating organizations assign low grades to such obligations. With over 1,200 holdings, including some riskier companies like casino operator Caesars Entertainment Inc. (CZR) and satellite television provider Dish Network Corp. (DISH), the iShares iBoxx $ High Yield Corporate Bond ETF invests exclusively in these distressed debts. You might get into hot water with HYG if the economy tanks or some of your borrowers stop paying. This riskier strategy, however, is currently yielding a 5.1% return.

3. iShares 1-3 Year Treasury Bond ETF

The iShares 1-3 Year Treasury Bond ETF is a low-risk investment option. This bond ETF manages around $28 billion, making it the largest. About 75 Treasury bonds are held by SHY, but their average duration is less than two years, so they regularly reinvest to avoid interest rate risks. They are U.S. Treasury bonds backed by the federal government, making them as safe as anything you can buy on Wall Street. The fund's 30-day yield is 4.4%, thanks to rate hikes, but even if that drops off in the long run, SHY remains a tempting option for conservative portfolios due to its steadfast strategy.

4. The Pimco Income Fund

One of the best options for investing in bonds is the Pimco Income Fund. About $120 billion in assets are managed by it right now. Investors are drawn to the fund primarily because of its attractive interest rate of 4.55% annually. The PONAX fund requires an initial commitment of $1,000 and has a higher cost ratio of 0.90%. However, depending on the state of the market, the annual distribution paid to shareholders has varied from 86 cents in 2015 to 43 cents in 2017.

Pimco Income Fund bond selections are rebalanced regularly to reflect shifting economic and market conditions. This method aids in making sure the PONAX fund can continue providing generous dividends to shareholders.

Additionally, the fund offers a respectable annualized return of 5.11% over a five-year time horizon, putting it in the upper third of its category regarding performance and returns to investors.

5. Vanguard Total International Bond ETF (BNDX)

Vanguard returns to the top spot on the list due to the company's wide selection of low-cost bond products. And for those wishing to diversify their holdings internationally, the Vanguard Total International Bond ETF is an excellent choice. To provide diversification, BNDX invests in high-quality bonds issued by governments and corporations in nations that are strong allies of the United States, including Germany, France, Canada, and Australia.

The rates on foreign bonds are frequently higher than those on U.S. bonds, which is one of their advantages. International fixed-income instruments can hedge against the improbable event of a U.S. default on debt commitments.

Bonds held by BNDX are denominated in a variety of currencies other than the U.S. dollar, and the fund uses derivatives to protect itself from fluctuations in the value of the dollar. The fund's management fee is minimal at just 0.07% per year, and investors receive a dividend of $0.05 per share every three months.